How can I check if a Stream is empty and throw an exception if it's not, as a non-terminal operation?
Basically, I'm looking for something equivalent to the code below, but without materializing the stream in-between. In particular, the check should not occur before the stream is actually consumed by a terminal operation.
public Stream<Thing> getFilteredThings() {
Stream<Thing> stream = getThings().stream()
.filter(Thing::isFoo)
.filter(Thing::isBar);
return nonEmptyStream(stream, () -> {
throw new RuntimeException("No foo bar things available")
});
}
private static <T> Stream<T> nonEmptyStream(Stream<T> stream, Supplier<T> defaultValue) {
List<T> list = stream.collect(Collectors.toList());
if (list.isEmpty()) list.add(defaultValue.get());
return list.stream();
}
